<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>05-作用域链案例</title>
</head>
<body>
    <script>
        // 作用域链： 函数使用变量的时候，采用就近原则

        //  案例1 ： 结果是几
        var num = 456;
        function f1(){
            var num = 123;
            function f2(){
                var num = 0;
                console.log(num);  // 0 站在目标出发，一层一层的往上查找
            }
            f2();
        }
        f1();

        // 案例2 ：结果是几？
        var a  = 1;

        function fn1(){
            var a = 2;
            var b = '22';
            fn2();

            function fn2(){
            var a = 3;
            fn3();

                function fn3(){
                        var a = 4;
                        console.log(a);  // 4
                        console.log(b);  // 22
                }
            }
        }
        fn1();
    </script>
</body>
</html>